1. Field of the Invention
This invention relates broadly to an improved method and apparatus employing optical type techniques for use in sensing and controlling juxtapositional relationships between an object and a sensing means (or structure with which the latter is associated) during relative movement therebetween and, when desired, also concurrently sensing other information (such as audio material, digitally encoded data, or the like) which is carried by the object.
In a more specific context, the invention will be illustrated and explained with particular reference to my currently preferred application thereof involving the precision play-back of audio material recorded on ordinary, grooved phonograph records without causing wear to the latter from any mechanical engagement between the pick-up or sensing means and the information carrying portions of the record. Other likely applications for the invention or significant parts thereof should become apparent to those skilled in the art, with reference to their particular needs or interests, from the disclosure herein of my own currently preferred application of the invention and the other comments which follow regarding its adaptability for exemplary other purposes.
2. Description of the Prior Art
The wear problem occasioned by conventionally sensing audio information recorded along the spiral groove of ordinary phonograph records (in the form of undulations in one or more of the longitudinal wall surfaces of the groove) by means of a "needle" riding in and mechanically engaging the groove (so as to be vibrated by the mentioned undulations at frequencies for reproducing the recorded sounds) has long been recognized. Repeated "playing" of such a record by means of a "needle" type pick-up inherently results in cumulative wearing away of portions of the recorded undulations, as well as possible and typical formation of false undulations, causing corresponding loss of fidelity in reproducing the audio information originally recorded and the insertion of various types of "noise". This problem has been especially critical with respect to the preservation of rare records for which replacements can no longer be obtained, but in general has affected all users of phonograph records of all kinds, who are naturally desirous of continued fidelity of reproduction of the recorded material over often substantial periods of use.
Much effort has been expended in another direction to lessen the amount of wear resulting from "needle" to record contact by developing more sensitive pick-ups that require a lesser force of mechanical engagement of the "needle" with the record, but the progress realized along those lines inevitably has provided only a partial improvement and is incapable of achieving a full solution to the problem, since wear and its consequences will continue on an at best retarded basis as long as the information sensing method employed involves moving mechanical engagement between a "needle" and the information carrying groove surfaces of the record.
The earliest suggestion of the use of any type of optical technique in the sensing of information from phonograph records, of which I am aware, is found in the Friebus U.S. Pat. Nos. 1,916,973, 1,877,447 and 1,891,227, of which the last two apparently represent intended improvements or extensions of the first. In U.S. Pat. No. 1,916,973, the problem of wear upon the record caused by the "needle" was mentioned in passing (although the problems primarily sought to be overcome apparently were the frequency limitations caused by the mechanical inertia of the "needle" load and the tendency of the type of "needles" then in use to themselves wear in a manner causing distortion of reproduction), and it was proposed to sense the sounds recorded as undulations in a wall of the record groove by means of an optical microscope and an associated photo-electric cell for detecting the flickering of light reflected from an internal wall of the groove caused by the undulations recorded therein; however, that patent appears entirely silent as to how the microscope might either be made to accurately track with the spiral groove of the record during rotation of the latter or be made to maintain a height or spacing from the typically varying level of the groove of an ordinary record upon a turntable for keeping the microscope in focus upon the wall of the groove from which variations in the intensity of reflected light due to the recorded undulations were to be sensed, both of which would have been critically essential to accurate or even practical operation of the arrangement proposed. In the latter respect, U.S. Pat. Nos. 1,877,447 and 1,891,227, which matured from applications filed after that from which U.S. Pat. No. 1,916,973 resulted, both utilize a guide pin riding in the information carrying groove of the record for groove tracking purposes and the bottom of a housing associated with the optical pick-up assembly riding on the grooved surface of the record for height controlling purposes. Thus, the mentioned Friebus patents, although neither providing nor seemingly even seeking a solution to the problem of eliminating wear upon records from moving mechanical engagement with the information carrying portions thereof, did suggest the possibility of employing an optical technique involving the sensing of the intensity of light reflected from a portion of a phonograph record carrying recorded information in the form of surface undulations as a means of sensing such recorded information.
Shortly after the mentioned Friebus U.S. Patents, the Williams U.S. Pat. No. 1,917,003 and the Hammond U.S. Pat. No. 1,967,882 proposed generally similar systems for optically sensing recorded information from phonograph records or the like based upon the intensity of light reflected from the recording grooves, except that the Williams and Hammond patents recognized the desirability of not having the guide pin used for tracking and height control purposes ride in the information carrying groove of the record and proposed the provision of special records having a separate guide groove for cooperating with the guide pin (the Williams patent also proposed the alternative of providing rollers for respectively engaging the surface and the edge of an ordinary record for height and tracking control purposes respectively). Thus, the Williams and Hammond patents show early appreciation of the importance both of avoiding wear-producing physical engagements with information carrying portions of records and of providing height and tracking control in systems where recorded information is to be sensed optically in terms of reflected light variations, but both proposed relatively crude mechanical means for accomplishing those functions that are of limited applicability or practicality.
The next development in the art of possible interest, of which I am aware, was the system for reproducing recorded sounds from grooved cylindrical records suggested by the Alexanderson U.S. Pat. No. 1,978,183. Although the system proposed by that patent does not provide variable height or spacing control between the record and the optical sensor for light reflected from the information carrying portions of the record (as I have found it essential to do for really accurate or practical reproduction with ordinary phonograph records or the like subject to non-planarities due to warping or manufacturing tolerances), such system does suggest splitting the reflected light into two components respectively directed to separate photo-electric cells, with the intensities of reflected light sensed by both cells jointly being cumulatively utilized as the achieved sensing of the information recorded on the track, and with the intensities respectively sensed by the two cells separately being utilized to control a device for axially shifting the cylindrical record to maintain tracking between the helical path of recorded information on the cylindrical record and a reflected light pick-up assembly being continuously moved along the length of the cylindrical record by a lead screw.
Following the Alexanderson patent, there appears to have been a virtual hiatus of approximately 30 years in the development of relevant systems or techniques, insofar as I am aware, during which the attention of those working in the field was apparently directed toward the previously mentioned goal of seeking merely an inherently partial solution to the problem of record wear due to "needle" contact therewith by improving the sensitivity of the transducer to which the "needle" was mechanically coupled and the mountings for the "needle" carrying pick-up head to permit the force of engagement of the "needle" with the information bearing portions of the record to be at least reduced.
The Rabinow U.S. Pat. No. 3,138,669 marked an apparent renewal of interest in the use of optical techniques for sensing recorded information from a phonograph record or the like, as well as a further attempt to suggest apparatus that might be practical for that purpose. That patent, like the much earlier Alexanderson patent, recognized the desirability of avoiding a guide pin of the sensor unit riding in a groove in the record for controlling tracking between an optical pick-up for recorded information and the groove or zone of the record carrying the recorded information to be sensed, and also sought to achieve such tracking function through optical means, namely, a light source which scanned continually back and forth across the information carrying groove, with the intensity of reflected light being sensed providing a component characteristic of the scanning reaching one edge of the groove for reversing the direction of scanning, and with the intensity sensings being essentially averaged to control the speed of a lead screw for maintaining tracking between the reflected light sensor and the groove.
The subsequent developments having some possible relevance, of which I am aware, appear to have concerned themselves with diverse miscellaneous aspects of systems employing optical techniques for sensing recorded information, but not to have really advanced the state of the art in any basic way sufficient to render the use of such techniques truely practical in any general sense.
The Dahlen U.S. Pat. No. 3,452,163 is of broad background interest as an illustrative confirmation that the skill of the art includes the ability to configure light paths to better satisfy space minimizing or other collateral requirements by means of lenses, mirrors, prisms, fiber optic rods and other known optical components, and the system proposed by that patent employs a pair of fiber optic rods with respectively associated sensors for separately sensing light reflected from the opposite sides of a recording groove, in order to handle stereo as well as monaural types of music bearing records, as well as to utilize the relative intensities of light reflected from the respective sides of the groove to provide a control signal for groove tracking purposes.
The Laue U.S. Pat. No. 3,666,896, the Zorn U.S. Pat. No. 3,975,630 and the Laub U.S. Pat. No. 4,044,378 further illustrate conventional techniques for configuring light paths with optical components. The system of the Laue patent employed a sensing "needle" riding in the information carrying groove, while those of the Zorn patent and the Laub patent utilized optical techniques for controlling tracking of the sensor with a zone of recorded information on the record. The Zorn patent also involved the employment of a non-grooved type of record on which information was recorded in the form of undulations or lateral displacements along the edge boundaries of a track or zone having different optical properties than the regions laterally adjacent thereto, although the system of that patent also employed laser type radiations.
The Mullin U.S. Pat. No. 4,079,261 confirms the continuing tendency in this art to rely upon mechanical means movably engaging the record for supporting an optical sensor in spaced relationship to the information carrying portions of the record by employing a wheel riding on the surface of the record for such purpose.
Insofar as I am aware, therefore, the present state of the art has heretofore failed to provide any really practical method or apparatus for the accurate and reliable sensing of information recorded in the form of undulations or lateral displacements of the boundaries of recording grooves or other information carrying zones wherein the sensing of not only the recorded information, but also of other information for controlling tracking and height, are derived entirely by optical techniques and without resort to some form of running engagement between parts associated with the sensor and portions of the record itself. Without eliminating such running engagements for controlling the height or spacing of the sensing unit relative to the information carrying portions of the record, the specific objectives of my preferred application simply cannot be realized. It is believed fair to further conclude that the systems previously employed for optical sensing of recorded information, in failing to provide other than relatively crude mechanical means for controlling height or spacing of the sensor relative to the recorded information being sensed from a record, and by failing to recognize that optical techniques could also be employed for that purpose, have thereby precluded such systems from achieving any full solution to the problem of eliminating wear while at the same time providing accurate fidelity of reproduction of recorded information, which inherently requires precise and typically variable positioning of the sensor relative to the record in order to maintain the required focused relationship with the information carrying area of a record characterized by typical warping, distortions or other lack of ideal planarity.